Some of the engines for use on motorcycles, for example, are provided with a V-belt type of CVT located on the axially outer side of the engine case and comprising a drive pulley attached to one end of the crankshaft, a driven pulley attached to one end of a transmission shaft placed parallel to the crankshaft, and a V-belt placed around the both pulleys.
A conventional engine with such a type of CVT is disclosed for example in a laid-open Japanese patent No. 3095024 constituted that part of the engine case is defined as a transmission case into which one end of the crankshaft and one end of the transmission shaft are made to extend in cantilever fashion, and that their distal ends are provided with the drive pulley and the driven pulley around which a V-belt is routed.
Another arrangement disclosed in a laid-open Japanese patent No. 2002-021989 is constituted that the transmission case is formed separately from the engine case, the fore-end portions of the crankshaft and the transmission shaft are supported through bearings with the transmission case, and air is introduced into the transmission case.
An example of V-belt disclosed in a laid-open Japanese patent No. Hei 07-027180 has a surface, to be in contact with the drive and driven pulleys, made of a resin member.
Still another example disclosed in a Japanese patent No. Hei 05-068398 is arranged that the lubricant oil chamber formed in the engine case is made to swell to be located below the V-belt type of CVT.
When the V-belt type of CVT is located on the side of the engine case, the temperature in the transmission case is likely to rise due to heat from the engine and heat generated by friction of the V-belt. The V-belt in particular is likely to deteriorate with the thermal effect and its insufficient durability is a problem. Therefore, the engine with the V-belt type of CVT on the side portion of the engine requires an arrangement that can prevent the temperature in the transmission case from rising, prevent the V-belt from deteriorating due to the temperature rise, and extend the durability of the V-belt.
An advantage of the present invention made in view of the situations with the prior art described above is to provide an engine that can prevent the temperature in the transmission case from rising, prevent the V-belt from prematurely deteriorating due to the temperature rise, and extend the durability of the V-belt.